From 18ac659dc6cabf7e543b7b2b2904ddedcf594597 Mon Sep 17 00:00:00 2001
From: David Vossel <dvossel@digium.com>
Date: Mon, 16 Mar 2009 17:49:58 +0000
Subject: [PATCH] Merged revisions 182281 via svnmerge from
 https://origsvn.digium.com/svn/asterisk/branches/1.4

........
  r182281 | dvossel | 2009-03-16 12:47:42 -0500 (Mon, 16 Mar 2009) | 7 lines

  Randomize IAX2 encryption padding

  The 16-32 byte random padding at the beginning of an encrypted IAX2 frame turns out to not be all that random at all.  This patch calls ast_random to fill the padding buffer with random data.  The padding is randomized at the beginning of every encrypted call and for every encrypted retransmit frame.

  Review: http://reviewboard.digium.com/r/193/
........


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@182282 65c4cc65-6c06-0410-ace0-fbb531ad65f3
---
 channels/chan_iax2.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/channels/chan_iax2.c b/channels/chan_iax2.c
index d8e00881e4..bda25b2371 100644
--- a/channels/chan_iax2.c
+++ b/channels/chan_iax2.c
@@ -1064,6 +1064,7 @@ static int acf_channel_write(struct ast_channel *chan, const char *function, cha
 static int decode_frame(ast_aes_decrypt_key *dcx, struct ast_iax2_full_hdr *fh, struct ast_frame *f, int *datalen);
 static int encrypt_frame(ast_aes_encrypt_key *ecx, struct ast_iax2_full_hdr *fh, unsigned char *poo, int *datalen);
 static void build_ecx_key(const unsigned char *digest, struct chan_iax2_pvt *pvt);
+static void build_rand_pad(unsigned char *buf, ssize_t len);
 
 static const struct ast_channel_tech iax2_tech = {
 	.type = "IAX2",
@@ -2547,6 +2548,9 @@ static int update_packet(struct iax_frame *f)
 
 	/* Now re-encrypt the frame */
 	if (f->encmethods) {
+	/* since this is a retransmit frame, create a new random padding
+	 * before re-encrypting. */
+		build_rand_pad(f->semirand, sizeof(f->semirand));
 		encrypt_frame(&f->ecx, fh, f->semirand, &f->datalen);
 	}
 	return 0;
@@ -4856,6 +4860,18 @@ static int iax2_trunk_queue(struct chan_iax2_pvt *pvt, struct iax_frame *fr)
 	return 0;
 }
 
+/* IAX2 encryption requires 16 to 32 bytes of random padding to be present
+ * before the encryption data.  This function randomizes that data. */
+static void build_rand_pad(unsigned char *buf, ssize_t len)
+{
+	long tmp;
+	for (tmp = ast_random(); len > 0; tmp = ast_random()) {
+		memcpy(buf, (unsigned char *) &tmp, (len > sizeof(tmp)) ? sizeof(tmp) : len);
+		buf += sizeof(tmp);
+		len -= sizeof(tmp);
+	}
+}
+
 static void build_encryption_keys(const unsigned char *digest, struct chan_iax2_pvt *pvt)
 {
 	build_ecx_key(digest, pvt);
@@ -4867,6 +4883,7 @@ static void build_ecx_key(const unsigned char *digest, struct chan_iax2_pvt *pvt
 	/* it is required to hold the corresponding decrypt key to our encrypt key
 	 * in the pvt struct because queued frames occasionally need to be decrypted and
 	 * re-encrypted when updated for a retransmission */
+	build_rand_pad(pvt->semirand, sizeof(pvt->semirand));
 	ast_aes_encrypt_key(digest, &pvt->ecx);
 	ast_aes_decrypt_key(digest, &pvt->mydcx);
 }
@@ -4933,7 +4950,7 @@ static int decode_frame(ast_aes_decrypt_key *dcx, struct ast_iax2_full_hdr *fh,
 		/* Decrypt */
 		memcpy_decrypt(workspace, efh->encdata, *datalen - sizeof(struct ast_iax2_full_enc_hdr), dcx);
 
-		padding = 16 + (workspace[15] & 0xf);
+		padding = 16 + (workspace[15] & 0x0f);
 		if (iaxdebug)
 			ast_debug(1, "Decoding full frame with length %d (padding = %d) (15=%02x)\n", *datalen, padding, workspace[15]);
 		if (*datalen < padding + sizeof(struct ast_iax2_full_hdr))